Laser desorption/vacuum ultraviolet photoionization of alkanethiolate self-assembled monolayers

Self assembled monolayers of straight-chain alkanethiolates (RS) on gold were studied by nitrogen laser desorption followed by vacuum ultraviolet (118 nm) photoionization of secondary neutrals in a time-of-flight mass spectrometer. The dominant feature of all photoionization mass spectra were the dimers (RSSR+) for all thiolates studied. No monomer ions (RS') were observed, in contrast with previous results from time-of-flight secondary ion and direct laser desorption mass spectrometry. Results are presented from experiments on the tetradecyl (C-14) and hexadecyl (C-16) mercaptan monolayers. Mixed C-14/C-16 monolayers generated both pure and mixed dimers, indicating a facile association between different monomer chain lengths. (C) 1997 by John Whey & Sons, Ltd.